You mean to save the world in its current state? If you want to save the world with all of the objects in the current location when you play the game, there's a way, but it's scary. If you want to save the world to its state before you started, you'll have to exit the play. There's also a preliminary way to save the world in its current event state, but arty and I are still working on it.

I really don't know. I usually just try to keep the filesize under 100kb so I can mass-produce the texture if I want to, but if it only occurs once in the world, it could be as large as you'd like without it taking up extra filespace in your world.